Nowaday all is focused on RDM mast, brands pushing them and sometime making rdm-only sails. Luckily my wonderful HSM sails can be rigged on both, SDM and RDM.
I've all (almost) Fiberspar masts and I've also bought two (400 and 430) RDM for wave situations, but i've kept also the SDM, as selling them I would have gain few money compared to their real value.
As Fiberspar declare and write on their mast al the specs (weight, carbon content, reflex), it's easy to see that:
- a SDM mast of same carbon conteht is LIGHTER than the same RDM
- a SDM mast of same carbon content has way HIGHER reflex index of the RDM with the same carbon content.
So, yes an RDM mast is or should be more durable and waveproof than a SDM, but to get the same reflex of the old sdm brother you have to choose a way higher carbon content, and the more the carbon content the more it's fragile...
More: a SDM mast can be easily carried with the top inside the base, so less room inside the mastbag, you cannot do this with RDM. I'm able to carry 4 sdm masts in 2 hard-case FS mast bags, and only two rdm more in their dedicated soft case (all then inside the big tube mastbag)...
More and more: for us (middle?-)heaviweight riders a 490 is often necessary, sometime also more (520) as we need bigger sails to plane in low thermal winds, but even a 460 RDM is hard to find, not to telly a longer one...
Finally I've seem that in my windsurfing is way easier to find flat or choppy water conditions, where I use only the SDM's as I get a more lively feeling. Using RDM surely I feel greater handling and a softer response, but when I want to push hard on lake or sea and there aren't waves or shorebreak, no question, SDM is the best choice!

I`ve no doubt SDM are tougher and perfectly OK on some sails (ie the ones designed for them) but I`ve given up on them !!!

Found both my NP and Tush (Search and Rocks 4.2 to 6`s) when rigged on SDM can hang on for another 5 mph wind or so.Initially and when moderately powered sails felt fine on RDM but when really pushing to max they definitely break up earlier than when rigged on equivalent SDM. They need longer booms on RDM and downhaul tension is less .

And I dont care what anybody says (or that IMCS says differently) RDM are NOT as stiff on equivalent lengths as SDM.

I can rig my 7.5 (GTX) on a Tush 75 430 with a massive extension and it feels ok. (not ideal) but try same with a RDM and its feels more like its rigged on a fishing rod. And my 430 RDM is 100% C !!!

Lay a 430 RDM and SDM out together over 2 stools. The RDM is definitely more flexible ! (Perhaps the Tush 75 are over stiff ???)

My RDM `s are now the spares and only use them reluctantly !!! (But I weigh 105k)

I only sail RDMs from 340 to 460 and I will not go back to SDM any time soon. Hot Sails Maui uses RDMs on their whole line and I am very happy with the bulletproof performance of the HOT RODS, from my Superfreak UL all the way to my race sails GPS. I actually love the fact that I can use the same mast on a Wave sail and on a Race Sail.

In general I think the consensus is that RDM are way stronger than SDM, and it is really a no brainer which one to choose in the waves or B&J. For the same carbon content they are indeed somewhat heavier, but keep in mind that a 90-100% carbon SDM is a big durability question mark, while a 90-100% RDM will probably outlast you. You should really compare a 75% SDM with a 90-100% RDM for durability (again not in the waves/B&J), and then the weight is the same. They are, in addition, easier to handle out and in the water (and easier to carry around, no need of a hard case, can be stored flat on top of each other, only one type of extension ... I saved a quite a lot of space in my van when I switched).

In terms of performance you need to rig a sail (more or less) on the mast it has been designed for, and if a mast feel too soft with a lot of extension for a 105Kg it just means ... it is the wrong mast for the application. Or if you use a race sail designed around a SDM you would be badly served by a RDM, and if you are a heavyweight a SDM + racesail is probably still the way to go, if you race. Same for big slalom sails (>8.5) or formula. For availability: Hot Sails has 92 and 97% carbon RDM in the lineup from 310 to 490 (65% carbon 340 to 430), and Loft Sails has a 520 in production.

I personally wish RDMs were the industry standard: this sport can use some simplification!

Rocks are designed to be used on RDM but I`ve found I need to change down earlier when rigged on RDM as opposed to SDM.Similar story with Search but suspect that been an older design was intended for SDM.Rock rigs on either. (In theory)

End of day we use what suits us. I sail waves/bump/jump all time and have yet to break a Tush 75 SDM. Last season all my Vmax`s were recorded on SDM and IMO sails have a larger wind range when rigged on them. Do suspect weight has a great deal; to do with it. At 105k I must be putting at least 30% more loading onto kit than Davide (at 70k). I can see great lines appearing in Rocks(and Search) when on RDM and overpowered.

I would never even consider a 460 RDM. Might even sell my 430 and 400 RDM`s from experiences I`ve had !! Cant see point in having a tougher mast if it results in a less efficient sail.. Before anyone buys RDM I would recommend you do a bit of testing with your rigs (at least rigging on them) before you commit and buy them.Especially if you are heavy.

The whole IMCS is thrown into disrepute. Compare even a 45% SDM with a 100% RDM and I`ll bet the SDM is stiffer !! (And probably as light !!!???)

Slightly off topic but has anyone felt the weight of Naish RDM`s !!! They are unbelievably heavy !!! Perhaps they are as stiff as claimed but should be at price they are ???

I would never even consider a 460 RDM. Might even sell my 430 and 400 RDM`s from experiences I`ve had !! Cant see point in having a tougher mast if it results in a less efficient sail..

Whatever ... you are 105Kg and you are basing your conclusion on one mast that does not fit you. There are whole lines of sails out there (e.g North or Hot) built around a single RDM mast covering 4.0/4.5 to 6.0/6.5 ... who knows if a RDM has more or less range than a SDM (whatever range means). And your observation that a more flexible mast has less upper range makes actually little sense, hard to tell what it is going on but it might not be what you think it is. A softer masts, SDM or RDM, should make overpowered sailing easier: you might loose some power, bottom end, but you gain control.

As far as weights, who really cares, but compare any numbers out there and you will see that a 70-80% SDM has roughly the same weight of a 90-98% RDM. To see a weight gain you have to use a 100% SDM or compare with a 65% RDM.

Forgot one thing.
What about the weight of rdm extensions??? I mean human-priced alloy type. The first time I got one I couldn't believe at it, 2x times than a sdm extension? And 2 time the price! I mean I've bought 4 rdm externsions, two common Ascan from Deutscheland, cheap and strong, but also a Chinook (something to complain about it), and a famous french one i don't remember
Standard: they are not. All 4 extensions are not snug fit in my Fiberspar, someone told me its because does exist a even smaller version, the super-rdm that is 2 mm less in inner diameter. I tried to solve the problem with a sheet of plastic, but the shorebreak of Rømø glued the nasty end cap of the Chinook inside, hard work to solve the problem..Never had similar problems with even old and weird sdm extensions
No debate that at least with wave mast rdm is the future, but I think that 20+ years of developement in SDMs were not useless, so RDMs need to still work on them, don't you agree?

"I`ve no doubt SDM are tougher and perfectly OK on some sails (ie the ones designed for them) but I`ve given up on them"

My observations are neither based on one mast or one set of sails but they are my observations !

Perhaps you should do some training; put on some weight and see if your observations on mine are justified !!!

A sailor at 70k can not comment on a sailors observations at 105 k and vice versa re over powered/stability. Your comments re flexible mast been more stable are simply wrong..

Flexible mast will twist off earlier to depower rig which is completely different to making sail stable ; your sails would be depowering too early for me which is exactly what is happening when I rig up on RDM.

Think about it Davide; when I`m sailing just normally powered up the sail is already operating at levels you would sense as overpowered !!!(It is nothing to do with ability/skil or anything itis just plain physics/weight.

The point is FOR ME RDM masts on the sails I am using are too flexible.

There has been a lot of market manipulation getting sailors to convert over to RDM. For some it is both a retrograde and expensive one.

Have you done any back to back testing recording boardspeed and windspeed with your sails on RDM and SDM ???? I have.

I've broken yesterday 2 100% carbon SDM 490 masts on the same day.
Bitter taste in my mouth ...
1 mast just snapped on the beach, while it was laying +/- 1 hour in the sun. I know I should not do it, but it happened.
The other snapped on the water after pumping, so I had to swim +/- half an hour.

Few years ago I was rigging a cambered NP on beach at Sotavento. Mast broke as I downhauled it (a NP X9) They brought me another. ( I was hiring kit luckiliy) and it broke again as I applied DH !!! Chose another rig !!!